The present invention relates to the preparation of novel bis(siloxane) derivatives of the chemical formula (I) which are useful in particular as an initiator for group transfer polymerization (hereinafter referred to as GTP). ##STR4##
Wherein R is either a straight or branched chain of aliphatic hydrocarbons, i.e., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, 2-methylbutyl, 3-methylbutyl group. Particularly, preferred aliphatic hydrocarbons are C.sub.1-4, R' is the same as R, n is integer of 0 to 2.
According to some prior arts as Polymer Preprint, Am. Chem. Soc. 27 (1), 161 1986, it discloses that GTP is a fundamentally new method for polymer formation. It involves the repeated addition of monomer to a growing polymer chain end which carries a reactive ketene silyl acetal group. During the addition, the silyl group transfers to incoming monomer regenerating a new ketene acetal function ready for reactive with more monomer, hence the name group transfer polymerization. Moreover, it also discloses that GTP has recently been reported to be a valuable new method for polymerization of .alpha.,.beta.-unsaturated esters, amides, and nitriles using ketene silyl acetals as initiators and certain Lewis acids or anions as catalysts.
As is well known in polymer chemistry, the GTP process is illustrated by Equation 1 for methylmethacrylate monomer (MMA). A catalyst, e.g., a sotuble bifluoride is required for the reaction to proceed. GTP provides "living polymer" rapidly at room temperature and offers new dimensions in the construction and design of polymer chains. ##STR5##
With certain initiators and catalysts, induction periods are noted, for example, with trimethyl silyl cyanide.
1-Alkoxy-1-(trimethylsiloxy)-2-methyl-1-alkenes, eg., Eq. (1) is the most powerful initiators for GTP. Large alkyl groups on the silicon lower the rate of polymerization. The --OR group on the initiator will be on one end of every polymer chain and can be used to introduce functionality. Compounds which can rearrange to ketene acetals such as .alpha.-silyl esters will also initiate GTP as Equation (2). ##STR6##
In addition, certain silyl derivatives which add to methacrylate, for example trimethylsilyl cyanide or trimethylsilyl methylsulfide, act as initiators, through generation of ketene acetals as Equation (3). The trimethylsilyl cyanide itself can be generated in situ by reaction of ammonium cyanide (R.sub.4 N.sup.+ CN.sup.-) with trimethylchlorosilicon. ##STR7##
Meanwhile, it is said that a variety of phosphorous terminated polymers can be synthesized by the use of phosphorous-containing ketene silyl acetals prepared by the thermal addition of silyl phosphites to .alpha.,.beta.-unsaturated esters. That is to say, Synthesis 1982, 497 and 1982, 915 disclose the preparation of phosphorous terminated polymers as Equation(4). ##STR8##
As can be seen in U.S. Pat. Nos. 4,417,034 and 4,508,880, well-known GTP initiators are .alpha.,.beta.-unsaturated ketene silyl acetals. Therefore acrylates, methacrylates, acrytonitriles can be polymerized and/or copolymerized by the use of aforementioned prior initiators.
There are some drawbacks in the prior arts to prepare an ABA type triblock copolymer by the use of the prior initiators. In order to prepare an ABA type triblock copolymer, in the beginning an A monomer alone is polymerized to be occuring a living A polymer which is preferably molecular weight to be wanted and then B monomer is copolymerized with the living A polymer. Finally an ABA triblock copolymer can be obtained by the reaction of an A monomer with the AB two blocks polymer. Therefore the process of the ABA type triblock copolymer in the prior arts is very complicated as the above-captioned description.